John McCain, who only days ago said it took an annual income of $5m (£2.5m) to be counted as truly rich, yesterday came under attack for admitting he had lost track of how many homes he owned.

In a godsend to the Democrats, the Republican was caught out when asked in an interview how many homes he owned. "I think ... I'll have my staff get to you," McCain told Politico, a Washington insider news website, and then muttered something about condominiums.

McCain's wife, Cindy, inherited one of America's biggest beer distribution firms and has an estimated fortune of $200m. The couple reportedly own seven homes in Arizona, California and Virginia, worth a combined total of about $13m. But Politico was told by his campaign they had four.

The Obama camp has been trying to draw attention to the McCains's wealth, in part to defend the Democrat against Republican charges that he is elitist.

The Democrats reacted yesterday on several fronts. In Chester, Virginia, Obama said his rival was out of touch.

"Somebody asked John McCain, 'How many houses do you have?' And he said, 'I'm not sure. I'll have to check with my staff.' True quote: I'm not sure, I'll have to check with my staff," said Obama, whose campaign went on to release a new television advert. Entitled Seven, after the number of McCain properties, it attacks the Republican record on the economy.

The Obama campaign also lined up events around the US to keep the controversy over McCain's comments alive.

The potential damage to McCain is great as there have been previous controversies over his wife's refusal to make a full disclosure about her finances, as well as his past comments. Earlier in the campaign, McCain said he believed the US economy remained strong, while an adviser had dismissed concern about the housing crisis and petrol prices as whining.